JP6968018B2 - Epoxy resin powder paint - Google Patents

Description

The present invention relates to an epoxy resin powder coating material suitable for bending after forming a coating film in the field of metal processing such as bus bars and steel pipes.

Epoxy resins have excellent mechanical properties, chemical resistance, corrosion resistance, and electrical properties, and are widely used as powder paints. As the epoxy resin powder coating, those containing a bisphenol A type epoxy resin, a phenol-based curing agent, dicyandiamide, an imidazole-based curing accelerator, or an imidazoline-based curing accelerator are known (Patent Document 1).

Japanese Unexamined Patent Publication No. 10-323616

Epoxy resin powder coating materials are widely used in the field of processed steel materials such as bus bars and steel pipes because of their excellent electrical properties and corrosion resistance. Since the processed steel material coated with the epoxy resin powder paint is used by bending it at an arbitrary angle at the time of construction, it is important to be able to perform the bending process without causing cracks in the coating film.

Above all, when applying epoxy resin powder paint to a bus bar, the paint film is bent without cracking, so the paint film is required to be flexible and at the same time to withstand thermal expansion due to energization. The film is also required to have heat resistance.

Further, since the conventional epoxy resin powder coating material has a slow curing speed and a long curing time, a quick-curing epoxy resin powder coating material is desired from the viewpoint of improving productivity.

Although the technique of Patent Document 1 satisfies the heat resistance, the crack resistance and the quick curing property at the time of bending do not satisfy the current requirements.
In particular, in recent years, there has been a demand for improved crack resistance during bending of coated reinforcing bars in a harsher environment, for example, in a cold region of 0 ° C. or lower, such as coating of reinforcing bars enclosed in reinforced concrete.

The present invention is an epoxy resin that can form a cured product having heat resistance and crack resistance during bending as a result of being imparted with high flexibility even at low temperatures while maintaining fast curing properties. A coating film consisting of a powder coating material and a method for producing the same, a cured product of the epoxy resin powder coating material, and having heat resistance and crack resistance during bending, and a processed steel material provided with the coating material are provided. The challenge is to provide.

The present inventors have described (D2) in a composition comprising (A), (B), (C), and (D) shown below, and (D) containing (D1) and (D2). The present invention has been completed by finding that the above-mentioned problems can be solved by adjusting the blending amount and the melting point.

That is, according to the present invention, an epoxy resin powder coating material having the following constitution is provided.
Further, according to the present invention, there are also provided a cured coating film obtained by thermally curing an epoxy resin powder coating having the following constitution, and a processed steel material in which the cured coating film is formed at least partially.
Further, according to the present invention, there is also provided a method for producing an epoxy resin powder coating material having the following constitution.

Below,
(A): A bisphenol type epoxy resin having an epoxy equivalent of 670 to 1200 g / eq,
(B): Rubber-modified epoxy resin,
(C): Bisphenol type phenol resin curing agent,
(D) Curing accelerator,
(D1): Imidazole derivative,
(D2): Addition reaction product of imidazole compound and epoxy resin,
And.
At this time, the present invention relating to the product is an epoxy resin powder coating material for forming a cured product.
Including (A), (B), (C), and (D),
(D) comprises (D1) and (D2), and is composed of a finely pulverized composition having a mass ratio of (D2) of 0.5 or more and 5.0 or less with respect to (D1): 1.
It is characterized by having a melting point of 60 to 90 ° C.

The present invention according to a manufacturing method is a method for manufacturing an epoxy resin powder coating material for forming a cured product.
Including (A), (B), (C), and (D),
(D) comprises (D1) and (D2), and a composition having a mass ratio of (D2) of 0.5 or more and 5.0 or less with respect to (D1): 1 having a melting point of 60 to 90 ° C. It is characterized by aging until it becomes fine and then finely pulverizing it.

In both of the above inventions, (B) can contain a butadiene / acrylonitrile rubber-modified epoxy resin having an epoxy equivalent of 800 to 1300 g / eq.

In both of the above inventions, the compounding ratio of (A) and (B) can be 92: 8 to 82:18.

In both of the above inventions, the total epoxy equivalent of (A) and (B) can be 750 to 1250 g / eq.

In the above-mentioned production method invention, aging can be performed under the conditions of 40 to 60 ° C. and 24 to 100 hours.

The epoxy resin powder coating material of the present invention contains (A), (B), (C), and (D), and (D2) in the composition containing (D1) and (D2) as (D). The blending amount and melting point of are adjusted. Therefore, while maintaining the quick-curing property, the coating film (cured product) after curing is imparted with high flexibility even at a low temperature (for example, 0 ° C. or lower) in addition to heat resistance. As a result, it is possible to form a cured product having heat resistance and crack resistance during bending.
That is, according to the present invention, a cured product having heat resistance and crack resistance during bending is formed as a result of imparting high flexibility even at a low temperature while maintaining quick curing property. An epoxy resin powder paint that can be used, a coating film that is composed of a cured product of the epoxy resin powder coating and has heat resistance and crack resistance during bending, and a processed steel material having the coating film. Can be provided.

The method of the present invention comprises a composition comprising (A), (B), (C), and (D) and having an adjusted blending amount of (D2) with respect to (D1) in (D), the melting point thereof. Is aged until it reaches a predetermined range. Therefore, while maintaining the quick-curing property, the above-mentioned performance, that is, heat resistance and high flexibility even at a low temperature are imparted, and as a result, a cured product having heat resistance and crack resistance during bending can be formed. Epoxy resin powder paint can be manufactured.

Hereinafter, the best embodiment of the present invention will be described, but the present invention is not limited to the following embodiments, and is based on ordinary knowledge of those skilled in the art to the extent that it does not deviate from the gist of the present invention. It is also within the scope of the present invention that the following embodiments have been appropriately modified, improved, or the like.

The epoxy resin powder coating of the present invention is (A): bisphenol type epoxy resin having an epoxy equivalent of 670 to 1200 g / eq, (B): rubber-modified epoxy resin, (C): bisphenol type phenol resin curing agent, (D). : Contains a curing accelerator. (D): The curing accelerator contains (D1): an imidazole derivative, and (D2): an addition reaction product of an imidazole compound and an epoxy resin.

The details of the powder coating material of the present invention will be described below.

<(A)>
As (A) used in the present invention, a conventionally known bisphenol type epoxy resin (an example of a glycidyl ether type epoxy resin having a phenol as a precursor) may be appropriately used according to the purpose of use. can.
As specific examples, bisphenol A type epoxy resin, bisphenol F type epoxy resin, brominated bisphenol A type epoxy resin, hydrogenated bisphenol A type or AD type epoxy resin and the like can be used.

Among these, it is preferable to use a bisphenol A type epoxy resin from the viewpoint of mechanical properties, chemical resistance, electrical properties, and corrosion resistance of the cured product.
Further, in the field where flame retardancy is required, it can be dealt with by using a brominated bisphenol type epoxy resin.

The epoxy equivalent of (A) is 670 to 1200 g / eq. When the epoxy equivalent is 670 g / eq or more, sufficient flexibility to withstand stress can be imparted, and when it is 1200 g / eq or less, strength and heat resistance can be maintained. In (A), two or more kinds may be used in combination so that the epoxy equivalent is in the range of 670 to 1200 g / eq.
Further, in consideration of curability, the softening point of (A) is preferably 80 to 120 ° C. When two or more types of (A) are used in combination, it is preferable to combine them so that the softening point is in the range of 80 to 120 ° C.

In the present invention, from the viewpoint of improving the flexibility at low temperature, the cresol novolac type epoxy resin, which is another example of the glycidyl ether type epoxy resin having phenols as a precursor, in the epoxy resin powder coating material. It is preferable not to select. Commercially available cresol novolak type epoxy resins include Epicron N-660, Epicron N-665, Epicron N-670, Epicron N-673, Epicron N-695 (all manufactured by DIC Corporation), EOCN-1020, and EOCN-102S. , EOCN-104S (above, manufactured by Nippon Kayaku Co., Ltd.) and the like.

<(B)>
As (B) used in the present invention, a rubber-modified epoxy resin is used. In the present invention, the rubber-modified epoxy resin is obtained by reacting (modifying) a rubber component with an epoxy group in the epoxy resin. In the present invention, the component (B) is not included in the component (A).
The epoxy resin is not particularly limited, and is, for example, a bisphenol type epoxy resin, a naphthalene type epoxy resin, a biphenyl type epoxy resin, a glycidylamine type epoxy resin, a ring type epoxy resin, a dicyclopentadiene type epoxy resin, and a phenol novolac type epoxy. Examples thereof include resins and orthocresol novolac type epoxy resins. A bisphenol type epoxy resin is preferable from the viewpoint of heat resistance, flexibility, and corrosion resistance. These may be used alone or in combination of two or more.

The rubber component refers to a rubber having a functional group that reacts with an epoxy group in an epoxy resin, and is not particularly limited. For example, butadiene rubber, acrylic rubber, silicone rubber, butyl rubber, olefin rubber, styrene rubber, NBR. (Butadiene / acrylonitrile rubber), SBR, IR, EPR and the like can be mentioned. Examples of the functional group of the rubber component include amino-modified, hydroxy-modified, and carboxyl-modified.
The product (B) used in the present invention is a product obtained by reacting these rubber components with an epoxy resin in an appropriate compounding ratio by a known polymerization method. From the viewpoint of imparting flexibility, an NBR-modified epoxy resin is used. Is preferable. The component (B) is preferably solid. These may be used alone or in combination of two or more.

The epoxy equivalent of (B) is preferably 800 to 1300 g / eq. By setting the epoxy equivalent to 800 g / eq or more, it is possible to impart sufficient flexibility to withstand more stress, and by setting it to 1300 g / eq or less, it is possible to maintain more strength and heat resistance. Is. In (B), two or more types may be used in combination so that the epoxy equivalent is in the range of 800 to 1300 g / eq.
Further, in consideration of curability, the softening point of (B) is preferably 80 to 120 ° C.
The concentration of the rubber component in (B) is preferably 85 to 95% from the viewpoint of flexibility.

The blending ratio of (A) and (B) is preferably in the range of 92: 8 to 82:18. By setting the compounding ratio of (B) to 8 or more, sufficient flexibility that can withstand more stress can be imparted, and by setting it to 18 or less, more strength and heat resistance can be maintained.

The total epoxy equivalent of (A) and (B) is preferably 750 to 1250 g / eq. By setting the total epoxy equivalent to 750 g / eq or more, sufficient flexibility to withstand stress can be imparted, and by setting it to 1250 g / eq or less, the strength and heat resistance can be further maintained. Is expected.

<(C)>
As (C) used in the present invention, a bisphenol type phenol resin curing agent is used. In the present invention, the bisphenol type phenol resin curing agent is obtained by reacting a bifunctional epoxy resin with an excess of bifunctional phenols, and contains phenolic hydroxyl groups at both ends but does not contain an epoxy group. ..
Examples of the bifunctional epoxy resin include bisphenol type epoxy resins such as bisphenol A type epoxy resin and bisphenol F type epoxy resin; diglycidyl ethers of alcohols such as hydrogenated bisphenol A, 1,6-hexanediol and polypropylene glycol; dimer. Diglycidyl esters such as acids; etc. A bisphenol type epoxy resin is preferable from the viewpoint of heat resistance, flexibility, and corrosion resistance. These may be used alone or in combination of two or more.

Examples of the bifunctional phenols include bisphenol A, bisphenol F, bisphenol S, bisphenol C, tetrabromobisphenol A, catechol, resorcin, hydroquinone and the like. Of these, bisphenol A or bisphenol F is preferable.
As (C), a bisphenol A type epoxy resin is used as the bifunctional epoxy resin, and bisphenol A or bisphenol F is reacted with this as the bifunctional phenols (bisphenol A type phenol resin curing agent) or bifunctional. Examples thereof include bisphenol F type epoxy resin used as an epoxy resin and bisphenol A reacted as bifunctional phenols (bisphenol F type phenol resin curing agent). (C) may be used in combination of two or more types.

The active hydroxyl group equivalent of (C) is preferably 200 to 500 g / eq. By setting the active hydroxyl group equivalent to 200 g / eq or more, sufficient flexibility to withstand stress can be imparted, and by setting it to 500 g / eq or less, strength and heat resistance can be maintained.

Normally, when a rubber component is blended, the heat resistance is significantly lowered, but by using (B) and (C) modified with an epoxy resin in combination, high flexibility is imparted to the cured coating film, and at the same time, heat resistance is obtained. Can be retained.

<(D)>
It is essential that (D) used in the present invention is a combination of a plurality of curing accelerators, and in particular, as (D), at least (D1) an imidazole derivative, (D2) an imidazole compound and an epoxy resin are used. It is used in combination with an addition reactant. In addition to this, the mass ratio of (D1) and (D2) is (D2): 0.5 or more and 5.0 or less (preferably 2.) with respect to (D1): 1 in all (D). It is also essential that it is 0 to 4.0). By using a specific combination of (D1) and (D2) in this mass ratio range, the curing rate can be adjusted, which is expected to improve the flexibility. If the ratio of (D1) is too large, the curing speed becomes too high, the crosslink density becomes high when the coating film is formed, and the coating film tends to become brittle. Further, if the ratio of (D1) is too small, the curing rate becomes insufficient, and the curing becomes insufficient when the coating film is formed.

(D1) is a compound in which a substituent or the like is introduced into imidazole, and examples thereof include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1,2-dimethylimidazole and the like. (D1) may be used in combination of two or more types. Above all, it is preferable to use 2-methylimidazole from the viewpoint of quick curing.

(D2) has a structure in which an imidazole compound is ring-opened and added to both terminal epoxy groups of the epoxy resin. The imidazole compound includes imidazole and an imidazole derivative. The epoxy resin includes a bisphenol type epoxy resin and the like. Examples of (D2) include an addition reaction product of 2-methylimidazole and a bisphenol A type epoxy resin, and an addition reaction product of 2-ethyl-4-methylimidazole and a bisphenol A type epoxy resin. (D2) may be used in combination of two or more types. Above all, it is preferable to use an addition reaction product of 2-methylimidazole and a bisphenol A type epoxy resin from the viewpoint of imparting higher flexibility at a low temperature to the cured coating film (cured product).

The epoxy resin powder coating material of the present invention has an epoxy resin other than the above components, a curing agent, a curing accelerator, a flame retardant, a coloring agent, a filler, a leveling agent, a dripping agent, and a coupling, as long as the effect is not impaired. Conventional auxiliary components such as an agent, a defoaming agent, a mold release agent, and a fluidity adjusting agent can be appropriately blended.
Examples of the flame retardant include phosphorus compounds, halogen compounds, antimony compounds, and metal hydroxides.

Examples of the colorant include titanium oxide, carbon black, phthalocyanine blue, copper and the like.
Examples of the filler include oxides such as silica, alumina, zirconia, titania, magnesia, ceria, itria, zinc oxide, iron oxide, barium titanium oxide, and alumina-silica composite oxide; silicon nitride, titanium nitride, and boron nitride. , Nitrides such as aluminum nitride; sparingly soluble ion crystals such as calcium fluoride, barium fluoride, barium sulfate; covalent crystals such as silicon and diamond; silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, titanium acid Potassium, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, boehmite, apatite, mulite, spinel, olivine, etc. , Or a compound containing these.

In the present invention, from the viewpoint of improving flexibility, it is preferable not to add an anti-yellowing agent, which can be contained in a conventional auxiliary component, to the epoxy resin powder coating material. Examples of the anti-yellowing agent include adipic acid dihydrazide, dicyandiamide, urea, aliphatic amines, aromatic amines, alicyclic amines and the like.

The epoxy resin powder coating material of the present invention can be produced, for example, by the following method.
(A), (B), (C), and (D) are blended, and if necessary, fillers, pigments, additives, and the like are added to perform melt kneading. The melt-kneading is preferably completed in a short time using an extruder or the like. The temperature at the time of melt-kneading depends on the type of filler to be blended, if necessary, but is preferably in the range of 90 ° C to 130 ° C. The melt-kneading time is preferably 5 minutes or less, more preferably 60 seconds or less.

As described above, all the components can be melt-kneaded at once, but some components can be melt-mixed in advance. For example, first, an epoxy resin component, a filler component, an additive such as a leveling agent and a coupling agent are melt-mixed in advance, then cooled and solidified, and the obtained mixture is coarsely pulverized. Next, a curing agent component, a curing accelerator component and a pigment component, and if necessary, a filler are dry-mixed with the obtained crude pulverized product, and the obtained mixture can be melt-kneaded. In this case, a kneader, a planetary mixer, or the like can be used for melting and mixing.
After melt-kneading, it is cooled and solidified, and the obtained composition (melt-kneaded product) is finely pulverized and classified to prepare, for example, an average particle size of 30 to 60 μm to obtain the powder coating material of the present invention. Be done.

The epoxy resin powder coating material of the present invention preferably has a melting point (Tm) of 60 ° C. or higher, preferably 70 ° C. or higher. If the melting point of the powder coating is 70 ° C. or higher, it can be expected that the performance of the sagging prevention and the edge cover will be improved. On the other hand, from the viewpoint of coating film uniformity, the melting point of the powder coating material is preferably 90 ° C. or lower, preferably 85 ° C. or lower. From the above viewpoint, the melting point of the powder coating material is usually 60 to 90 ° C., preferably 65 to 90 ° C., and more preferably 70 to 85 ° C. The melting point of the powder coating material is determined by DSC (temperature range 25 ° C. to 280 ° C., heating rate 10 ° C./min).

The melting point of the powder coating material can be adjusted to the above range by aging the composition (melt kneaded product) obtained by melt-kneading the compound and cooling and solidifying it before pulverizing. The aging in the present invention refers to a step of slowly advancing the reaction with the epoxy resin, the curing agent and the curing accelerator, and aging the melt-kneaded product so that the melting point is within the above range.

The aging conditions of the melt-kneaded product are not particularly limited, but the temperature is preferably in the range of 40 to 60 ° C, more preferably 50 to 55 ° C. The time is preferably 24 hours or more, more preferably 60 hours or more, further preferably 72 hours or more, preferably 100 hours or less, still more preferably 90 hours or less.
In the present invention, the melting point of the finally obtained powder coating material is adjusted by aging the melt-kneaded product before it is finely pulverized, thereby improving the performance of the powder coating material such as quick curing and sagging prevention. Be expected.

The type and shape of the member to which the epoxy resin powder coating of the present invention is coated is not particularly limited, but the powder coating of the present invention is particularly bent at an arbitrary angle during construction after the powder coating is applied. It is suitably used for processed steel materials, and the effects of the present invention are effectively exhibited.
That is, since the epoxy resin powder coating material of the present invention has good followability to the processed steel material to be bent, for example, it can be used for rod-shaped objects, linear objects, tubular objects, corrugated sheet objects and the like. It is preferably used.

In the epoxy resin powder coating material of the present invention, a conventionally known coating method can be appropriately used according to the purpose of use thereof. For example, a fluidized bed method, an electrostatic fluidized bed method, a corona charging method, a friction charging method and the like can be mentioned. Among these, the fluid dipping method is preferable in order to obtain a coating film having a sufficient film thickness.

Hereinafter, the present invention will be specifically described based on experimental examples (including Examples and Comparative Examples), but the present invention is not limited to these Examples. In the following description, "part" means "part by mass" and "%" means "% by mass".

1. 1. Fabrication of epoxy resin powder paint
[Experimental Example 1]
Epoxy resin A1, epoxy resin 3, epoxy resin B5, curing agent C1, curing accelerator D1 and curing accelerator D2 were blended in the mass ratios shown in Table 1 and melt-kneaded at 105 ° C to 120 ° C with an extruder. The kneading time at this time was 20 seconds or less. The composition after melt-kneading was cooled and solidified, aged under the conditions shown in Table 1, and then finely pulverized to obtain a powder coating material.

The details of each of the above components are as follows.
Epoxy resin A1: Bisphenol A type epoxy resin with an epoxy equivalent of 910 g / eq and a softening point of 96 ° C (jER1004, manufactured by Mitsubishi Chemical Corporation).
Epoxy resin 3: Epoxy equivalent 634 g / eq, bisphenol A type epoxy resin with a softening point of 78 ° C (jER1002, manufactured by Mitsubishi Chemical Corporation)
Epoxy resin B5: Epoxy equivalent 950 g / eq, butadiene-acrylonitrile rubber-modified epoxy resin with a softening point of 95 ° C. (EPOX MK-SR35K, manufactured by Printec)

-Curing agent C1: Bisphenol A type phenol resin curing agent with active hydroxyl group equivalent of 333 g / eq (JER Cure 170, manufactured by Mitsubishi Chemical Corporation)

-Curing accelerator D1: 2-methylimidazole (Curesol 2MZ-H, manufactured by Shikoku Chemicals Corporation)
-Curing accelerator D2: Addition reaction product of 2-methylimidazole and bisphenol A type epoxy resin (Epicure P-101, manufactured by Yuka Ciel Epoxy Co., Ltd.)

[Experimental Examples 2, 3, 4, 4-2, 5-24]
A powder coating material was obtained in the same manner as in Experimental Example 1 except that the compounding components and / or the compounding amount and the aging conditions were changed as shown in Tables 1 to 3.

In Experimental Example 2, as (A), the epoxy resin A1 and the epoxy resin 3 were used in combination so that the epoxy equivalent was 750 g / eq. Further, in order to match the equivalent ratios, the curing agent C1 and the flame retardant were blended at the mass ratios shown in Table 1. In Experimental Example 3, the epoxy resin A1 and the epoxy resin 3 were used in combination as (A) so that the epoxy equivalent was 799 g / eq. Further, in order to match the equivalent ratio, the curing agent C1 was blended at the mass ratio shown in Table 1. In Experimental Example 5, the epoxy resin A1 and the epoxy resin 2 were used in combination as (A) so that the epoxy equivalent was 1017 g / eq. Further, in order to match the equivalent ratio, the curing agent C1 was blended at the mass ratio shown in Table 1. In Experimental Example 6, as (A), the epoxy resin A1 and the epoxy resin 2 were used in combination so that the epoxy equivalent was 1404 g / eq. Further, in order to match the equivalent ratio, the curing agent C1 was blended at the mass ratio shown in Table 1.

In Experimental Example 8, as (A), the epoxy resin A1 and the epoxy resin 2 were used in combination so that the epoxy equivalent was 1343 g / eq. Further, in order to match the equivalent ratio, the curing agent C1 was blended at the mass ratio shown in Table 2.

In Experimental Examples 20 to 24, the epoxy resin A1 and the epoxy resin 3 were used in combination as (A) so that the epoxy equivalent was 799 g / eq, as in the case of Experimental Example 3. Further, in order to match the equivalent ratio, the curing agent C1 was blended at the mass ratio shown in Table 3.

The components other than the components used in Experimental Examples 2 and later shown in Tables 1 to 3 are as follows.
Epoxy resin 2: Epoxy equivalent 1880 g / eq, bisphenol A type epoxy resin with a softening point of 123 ° C (jER1007, manufactured by Mitsubishi Chemical Corporation)
Epoxy resin 4: Epoxy equivalent 625 g / eq brominated bisphenol A type epoxy resin (jER5051, manufactured by Mitsubishi Chemical Corporation)
-Epoxy resin 6: Urethane (non-rubber) modified epoxy resin with an epoxy equivalent of 230 g / eq (ADEKA RESIN EPU-78-11, manufactured by ADEKA)

-Curing agent C2: Bisphenol A type phenol resin curing agent with active hydroxyl group equivalent of 222 g / eq (JER Cure 171N, manufactured by Mitsubishi Chemical Corporation)
-Curing agent 3: Novolac type phenol resin curing agent with active hydroxyl group equivalent of 106 g / eq (Tamanol 759, manufactured by Arakawa Chemical Co., Ltd.)

-Curing accelerator 3: Triphenylphosphine (PP-360, manufactured by Kay Kasei Co., Ltd.)
・ Anti-yellowing agent: Adipic acid dihydrazide (ADH, manufactured by Otsuka Chemical Co., Ltd.)

2. 2. Evaluation Various characteristics (melting point, quick-curing property) of the powder coating materials obtained in each experimental example were evaluated by the methods shown below. In addition, various properties (flexibility, heat resistance) of the cured product (thermosetting coating film) of the powder coating obtained in each experimental example were evaluated by the methods shown below. The results are shown in Tables 1-3.

(2-1) Melting point For the powder coating obtained in each experimental example, a differential scanning calorimetry device (trade name: DSC6220, SI Nanotechnology, Inc.) was used to raise the temperature at 10 ° C./min and the measurement temperature range. : Differential scanning calorimetry (DSC) was performed on a 3 mg to 8 mg sample sealed in an aluminum pan under the conditions of room temperature (25 ° C.) to 280 ° C. and a flow rate of 40 ± 20 ml / min under a nitrogen atmosphere. From the obtained results, the temperature at which the energy change accompanying the phase transition occurs (endothermic reaction peak temperature) was defined as the melting point.
In addition, the powder coating material obtained in each experimental example was heated from room temperature, the temperature was stabilized for 30 seconds each time it was heated at 10 ° C., and each time it was observed with a polarizing microscope whether or not a phase transition had occurred was observed in a cross Nicol state. (100 magnification). If a phase transition is observed near the same temperature as the melting point obtained by the DSC, the temperature of the endothermic reaction peak obtained by the DSC is taken as the melting point. Further, when the endothermic reaction peak was not obtained by the DSC and the state of the phase transition was observed by the observation with a polarizing microscope, the observed temperature was also taken as the melting point.

(2-2) Fast-curing property The fast-curing property was evaluated according to the following criteria by measuring the gelation time.
Approximately 0.05 to 0.1 g of the powder coating obtained in each experimental example was placed in the circular recess of a hot plate held at 150 ° C., and the mixture was stirred with a stirring rod until the threads were not pulled, that is, for gelation. The time (seconds) to reach was measured. It was measured according to JIS C 2104.

The evaluation criteria for quick curing are as follows.
◯: Gelling time is less than 100 seconds ×: Gelling time is 100 seconds or more

(2-3) Flexibility The flexibility was measured according to the following criteria by measuring the Eriksen value.
The powder coating material obtained in each experimental example was applied to a single plate having a thickness of 1 mm and a width of 100 mm by a flow dipping method so as to have a film thickness in the range of 150 to 280 μm. The painting time was 1 to 3 seconds. It was cured at 170 ° C. for 90 seconds in a constant temperature blower preheated at 210 ° C. for 15 minutes or longer. Immediately after curing, it was immersed in water for 30 seconds and cooled to obtain a test plate. The obtained test plate was evaluated by the Eriksen test according to JIS Z 2247. It was carried out at a pushing speed of 5 to 10 mm / min, and the pushing depth when cracks occurred was taken as the Eriksen value.

The evaluation criteria for flexibility are as follows.
⊚: Eriksen value is 10 mm or more ○: Eriksen value is 9 mm or more and less than 10 mm ×: Eriksen value is less than 9 mm × ×: The paint is difficult to adhere to the adherend and the coating film is uneven, so the test could not be performed. thing

(2-4) Heat resistance The heat resistance was evaluated according to the following criteria.
The temperature rise rate of the cured product obtained by preheating the constant temperature blower at 210 ° C for 15 minutes or more and curing the powder coating obtained in each experimental example at 170 ° C for 90 seconds using a DSC (Differential Scanning Calorimeter). Under the conditions of: 10 ° C./min and measurement temperature range: 25 ° C. to 280 ° C., DSC measurement was performed on each sample weighed about 3 to 8 mg, and the glass transition temperature was measured. Hereinafter, the glass transition temperature is defined as Tg.

The evaluation criteria for heat resistance are as follows.
◯: Tg is 90 ° C. or higher ×: Tg is less than 90%

3. 3. Consideration
As shown in Table 1, the powder coating materials of Experimental Examples 2 to 5 contain (A), (B), (C), (D1) and (D2) in an appropriate range, and have appropriate aging. As a result, the melting point was within the proper range. As a result, the powder coating material was excellent in quick curing property. Further, the obtained cured coating film had excellent heat resistance and flexibility. In particular, the powder coating materials of Experimental Example 3 and Experimental Example 4 had melting points of 70 ° C. and 75 ° C., respectively, and had extremely excellent flexibility when formed into a coating film.
On the other hand, the powder coating materials of Experimental Examples 1 and 6 did not have a melting point in an appropriate range. The powder coating material of Experimental Example 1 has a low melting point, has a high crosslink density and tends to harden the coating film as compared with Experimental Examples 2 to 5, and therefore has poor flexibility when formed into a coating film. On the other hand, the powder coating material of Experimental Example 6 has a high melting point, the coating material does not easily adhere to the adherend, and the coating film becomes non-uniform, so that it cannot be put into practical use. Further, since the crosslink density is low, the Tg is low and the heat resistance is inferior when the coating film is formed.

Next, as shown in Table 2, in the powder coating material of Experimental Example 7, the total epoxy equivalent of the (A) epoxy resin was less than 670 g / eq. As a result, the flexibility was inferior when the coating film was formed as compared with Experimental Example 4.
Further, in the powder coating material of Experimental Example 8, the total epoxy equivalent of the (A) epoxy resin exceeded 1200 g / eq. As a result, as compared with Experimental Example 4, the Tg was low and the heat resistance was inferior when the coating film was formed.

Further, the powder coating material of Experimental Example 9 did not contain (B) a rubber-modified epoxy resin. As a result, the flexibility was inferior when the coating film was formed as compared with Experimental Example 4.
Further, the powder coating material of Experimental Example 10 used a urethane-modified epoxy resin instead of the rubber-modified epoxy resin (B). As a result, as compared with Experimental Example 4, the Tg was low and the heat resistance was inferior when the coating film was formed.

Further, the powder coating material of Experimental Example 11 used a novolak type phenol resin curing agent instead of the (C) bisphenol type phenol resin curing agent. As a result, the flexibility was inferior when the coating film was formed as compared with Experimental Example 4.
Further, the powder coating material of Experimental Example 12 used triphenylphosphine as a curing accelerator instead of (D1) an imidazole derivative and (D2) an addition reaction product of an imidazole compound and an epoxy resin. As a result, the quick-curing property was inferior to that of Experimental Example 4, and the curing was insufficient when the coating film was formed, so that the flexibility and heat resistance were inferior.

Further, the powder coating material of Experimental Example 13 did not contain the (D1) imidazole derivative and used only the (D2) imidazole compound as the curing accelerator. As a result, the quick-curing property was inferior to that of Experimental Example 4, and the curing was insufficient when the coating film was formed, so that the Tg was low and the heat resistance was inferior.
Further, the powder coating material of Experimental Example 14 did not contain the (D2) imidazole compound as the curing accelerator, and used only the (D1) imidazole derivative. As a result, as compared with Experimental Example 4, the curing rate was high, and the crosslink density became too high when the coating film was formed, so that the flexibility was inferior.

Further, the powder coating material of Experimental Example 15 contained (A): (B) in a smaller amount of (B) than 92: 8. As a result, the flexibility was lower when the coating film was formed as compared with Experimental Example 4, but there was no problem in practical use.
Further, the powder coating material of Experimental Example 16 contained (A): (B) in a larger amount of (B) than 82:18. As a result, as compared with Experimental Example 4, the Tg was low and the heat resistance was low when the coating film was formed, but there was no problem in practical use.

Further, the powder coating material of Experimental Example 17 contained 1 compound of (D2) with respect to 1 of (D1), and the compounding amount of (D1) was larger than that of Experimental Example 4. As a result, the crosslink density was higher than that of Experimental Example 4, and the flexibility was low when the coating film was formed, but there was no problem in practical use.
Further, the powder coating material of Experimental Example 18 is a mixture of (D1) 1 and 5 (D2), and the amount of (D1) is the same as that of Experimental Example 4 and the amount of (D2) is compounded. Was a lot. As a result, it is considered that the reactivity was generally higher and the cross-linking density was higher than that of Experimental Example 4, and the flexibility was low when the coating film was formed, but there was no problem in practical use. Met.

Further, the powder coating material of Experimental Example 19 was a powder coating material of Experimental Example 4 containing an anti-yellowing agent. As a result, adipic acid dihydrazide, which is an anti-yellowing agent, is involved in the curing reaction and tends to harden the coating film, so that the flexibility is inferior when the coating film is formed as compared with Experimental Example 4. However, there was no problem in practical use.
Further, although not shown in Table 2, when the powder coating material of Experimental Example 3 was evaluated by containing an anti-yellowing agent, the same tendency as that in the case of comparison between Experimental Example 4 and Experimental Example 19, that is, an experiment The one containing the anti-yellowing agent in Example 3 was inferior in flexibility when formed into a coating film as compared with Experimental Example 3. However, there was no problem in practical use.

Next, as shown in Table 3, the powder coating materials of Experimental Examples 20 to 24 had improper aging conditions and had a melting point outside the appropriate range. The powder coating materials of Experimental Examples 20 to 22 have a melting point of less than 60 ° C., are inferior in quick-curing property as compared with Example 3, and are insufficiently cured when formed into a coating film. As a result, the flexibility and Tg were low and the heat resistance was low.
Further, the powder coating materials of Experimental Examples 23 and 24 have a melting point of more than 90 ° C., and as compared with Example 3, the coating material is less likely to adhere to the adherend and the coating film becomes non-uniform, so that it is practically used. It became unbearable.

Claims (9)

Epoxy resin powder coating for forming a cured product,
Including (A), (B), (C), and (D) shown below,
(D) contains (D1) and (D2) shown below, and is composed of a finely divided composition having a mass ratio of (D2) of 0.5 or more and 5.0 or less with respect to (D1): 1. Epoxy resin powder paint with a melting point of 60 to 90 ° C.
(A): Epoxy equivalent 670-1200 g / eq bisphenol type epoxy resin (B): rubber modified epoxy resin (C): bisphenol type phenol resin curing agent (D): curing accelerator (D1): imidazole derivative (D2) : Addition reaction product of imidazole compound and epoxy resin (B) is the epoxy resin powder coating according to claim 1, which comprises a butadiene / acrylonitrile rubber-modified epoxy resin having an epoxy equivalent of 800 to 1300 g / eq. The epoxy resin powder coating material according to claim 1 or 2, wherein the compounding ratio of (A) and (B) is 92: 8 to 82:18. The epoxy resin powder coating material according to any one of claims 1 to 3, wherein the total epoxy equivalent of (A) and (B) is 750 to 1250 g / eq. The epoxy resin powder coating material according to any one of claims 1 to 4, wherein the gelation time measured according to JIS C 2104 is less than 100 seconds. Obtained by thermosetting the epoxy resin powder coating according to any one of claims 1 to 5.
The indentation depth (Elixin value) at the time of cracking by the Elixin test (intrusion speed 5 to 10 mm / min) according to JIS Z 2247 is 9 mm or more, DSC (temperature range 25 ° C to 280 ° C, temperature rise rate 10 ° C /). A cured coating film with a glass transition temperature of 90 ° C or higher due to minute). A processed steel material on which the cured coating film according to claim 6 is formed at least in part. A method for producing an epoxy resin powder coating material for forming a cured product.
It comprises (A), (B), (C), and (D) shown below, (D) comprises (D1) and (D2), and the mass ratio of (D2) to (D1): 1 is A method for producing an epoxy resin powder coating material, which comprises aging a composition having a temperature of 0.5 or more and 5.0 or less until its melting point reaches 60 to 90 ° C. and then finely pulverizing the composition.
(A): Epoxy equivalent 670-1200 g / eq bisphenol type epoxy resin (B): rubber modified epoxy resin (C): bisphenol type phenol resin curing agent (D): curing accelerator (D1): imidazole derivative (D2) : Addition reaction product of imidazole compound and epoxy resin The method for producing an epoxy resin powder coating according to claim 8, wherein the epoxy resin powder coating material is aged under the conditions of 40 to 60 ° C. and 24 to 100 hours.